Knife sharpener



FIG. 1 is an upper perspective view of the knife sharpener showing my design.

FIG. 2 is a front elevation view thereof;

FIG. 3 is back elevation view thereof;

FIG. 4 is a side elevation view thereof;

FIG. 5 is an opposite side elevation view thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom plan view thereof.

The broken lines in FIGS. 1, 2, and 5 are directed to portions of the knife sharpener that form no part of the claim. 

The ornamental design for a knife sharpener, as shown and described. 